The present invention relates to an ink jet printer which ejects pressurized ink from an ink ejection head or nozzle to print out characters or like data on a sheet of paper and, more particularly, to an apparatus for removing air which may be entrained by the ink fed to the ink ejection head.
In an ordinary ink jet printer, ink is fed under pressure to an ink ejection head and pressure oscillation of a given frequency and amplitude is applied to the ink ejection from a nozzle of the head. As soon as the ink jet separates into a droplet, it is effected by an electric field to be charged thereby and then deflected by a deflecting electric field to impinge on a paper sheet.
Ink in this type of printer is apt to entrain air before reaching the ink ejection head. Air contained in the ink would disturb or practically disenable ink ejection and thereby prevent droplets from being regularly formed at predetermined intervals and each with a predetermined amount, thus effecting the quality of the resulting images on the paper sheet. An implement heretofore known for solving this problem comprises an air collector which is communicated through a valve to an ink passageway, which extends from the ink pressurizing source to the nozzle, so that air accumulated in an upper section of the ink passageway may be gathered in the air collector (as disclosed in Japanese Patent Publication Nos. 52-15178/77 and 52-15333/77). However, once the air collector becomes filled up with air, no more air can be accommodated therein. Replacement of the air collector or the discharge of air from the air collector requires disproportionate time and labor and even the chance may be lost. Concerning Japanese Patent Publication No. 52-15178/77, another drawback is that the ink continuously outflows from the nozzle over a substantial period of time even after the deactivation of a pump, thereby smearing various structural elements around the nozzle. As to Japanese Patent Publication No. 52-15333/77, on the other hand, it requires a number of structural elements as represented by three sets of valves.
Meanwhile, the ink temperature effects the ink viscosity and thereby the mass of an ink droplet as well as the amount of charge deposited thereon, which as a whole will vary the amount of deflection. It is therefore desirable to maintain the ink at a constant temperature and this has been implemented by a heater which is installed in an ink reservoir or in an ink passageway. Preferably, the heater should be located as close to the head as possible.